遍历字符时如何在UILabel中显示字符？ [英] How do I display characters to a UILabel as I loop through them?

问题描述

我有一个在单独的线程上执行循环的方法。出于对我的程序有效的原因，我使用以下方法调用此方法，

I have a method that performs a loop on a separate thread. For reasons that work for my program I call this method using,

[self performSelectorInBackground:@selector(myMethod:) withObject:arg];

以及实际方法，

- (void)myMethod:(NSString *)arg {
    NSAutoreleasePool *pool = [NSAutoreleasePool new];
    for (int i = 0; i < [arg length]; i++) {

    unichar ch = [arg characterAtIndex:i];
    NSLog(@"Processing character %c",ch);

    NSString *currentChar = [[NSString alloc] initWithFormat:@"%c", ch];
    viewController.outputLabel.text = currentChar;
    [currentChar release];


    switch (ch) {
    //Do my stuff
    }

    [pool release];

}

现在我的问题是，只有最后处理的字符会显示在我的UILabel中，但是当我在运行程序时检查控制台时，由于正在处理字符，它们正一一显示在控制台上（使用NSLog）。这正是我想在标签上看到的行为。

Now my problem is that ONLY THE LAST character that was processed gets displayed in my UILabel, yet when I check my console while running the program, as the characters are being processed they are being displayed to the console one-by-one (using NSLog). This is exactly the behavior I'd like to see going on in my label.

另外，我应该告诉您，每次处理字符时（在开关中语句）至少有一点延迟，因为我至少要调用 [NSThread sleepForTimeInterval：delayTime];

Also I should tell you that every time I'm processing a characters (in the switch statement) there is a least a slight delay because i'm calling [NSThread sleepForTimeInterval:delayTime]; at least a couple times.

推荐答案

您正尝试从主线程以外的线程更新视图（您的 outputLabel），这是不允许的。

You are attempting to update a view (your "outputLabel") from a thread other than the main thread, and this is not allowed.

您需要强制从主线程进行更新。您可以通过调用

You need to force the update to happen from the main thread. You can do this by calling

- (void)performSelectorOnMainThread:(SEL)aSelector withObject:(id)arg waitUntilDone:(BOOL)wait

所以，像这样：

[viewController.outputLabel performSelectorOnMainThread: @selector( setText: ) withObject: currentChar waitUntilDone: YES];

这篇关于遍历字符时如何在UILabel中显示字符？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！